Available as vibration damping materials for absorbing vibration are those of the nonconstraining type which are merely attached each as a superposed layer to vibration sources, and those of the constraining type which comprise a layer to be attached over one surface thereof to the vibration source and a constraining layer resistant to deformation and superposed on the other surface of the layer.
The main factor enabling the nonconstraining vibration damping material to exhibit vibration damping properties is the storage modulus (E′) relating to the elastic properties of the material, so the nonconstraining vibration damping material consists mainly of a resin component and a metal powder or inorganic material. However, the nonconstraining vibration damping material needs to have such flexibility as to readily permits the material to be laminated to the vibration source. For this reason, there is a limitation to the vibration damping properties.
On the other hand, the main factor enabling the constraining vibration damping material to exhibit vibration damping properties is tan δ (=E″/E′) (wherein E″ is the loss modulus relating to the viscous properties of the material). The constraining vibration damping material consists mainly of a rubber or a mixture of resin and rubber. However, the upper limit of tan δ is about 1.0 to about 1.2 and is not a level affording satisfactory vibration damping properties. Still higher vibration damping properties are desired for constraining vibration damping materials to exhibit higher sound insulation performance.
Proposed as a resin composition for vibration damping materials is a composition for high attenuation materials which comprises a base polymer material having a polar side chain such as chlorinated polyethylene, and chlorinated paraffin having 20 to 50 carbon atoms on average with admixed with the polymer material (JP-A 11-80562). The vibration damping material obtained is nevertheless limited to about 1.3 to about 1.5 in tan δ and fails to exhibit outstanding vibration damping performance.
On the other hand, generally used as sound insulating materials are metalic materials or inorganic materials having a larger specific gravity, such as lead sheets (11.3 in specific gravity), asphalt having iron particles incorporated therein, concrete, gypsum boards, etc. However, these sound insulating materials fail to exhibit high vibration damping performance and are not satisfactory in both vibration damping performance and sound insulation performance.
The object of the present invention is to provide sound insulating members exhibiting high vibration damping performance and high sound insulation performance, a vibration damping material for affording such members and a resin composition for forming the vibration damping material.